Making Rock Candy

Making Rock Candy

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Explore the deeper level of patterns in our world with a tasty and beautiful project!


Making your own rock sugar is a classic home experiment, but what makes it mathematical? Analyzing patterns in our world is a key skill of mathematicians, and exploring the patterns of molecular structures with this activity is a great way for young students to explore math and science with a tasty reward!


This project is for 2 sticks of rock candy, for which you will need:

  • 3 Cups of Sugar (use a higher quality, name-brand sugar)
  • 1 Cup of Water
  • Hot plate or stove (with parental assistance!)
  • Pot
  • Stirring spoon
  • 2 Popsicle sticks
  • 2 Glass Jars
  • 2 Clothespins
  • Food Coloring

Project Background

Patterns are not just the visual representations of colors and shapes (like stripes, polka dots, or a wall of bricks); patterns also explain how our entire world is built with molecules - the tiny building blocks of our world that go beyond what our naked eye can see. Molecules are the Lego blocks of life.


Crystals and gemstones have a very special trait about them: their molecules come together to create patterns. Each type of molecular pattern is what defines different types of crystals and makes them unique. 


Here is a very simple, 3-D pattern of a crystal's molecules that you see every day in your house:

It's salt!
Look at each smaller cube of molecules within the larger cube. Do you see the same cube of molecules over and over again? This crystal - that is, common salt - is created by this special formation of molecules repeating over and over again in 3 dimensions!

Here's another, more complicated pattern of molecules that make up another crystal:
This one is garnet! The beautiful gemstone we use in fancy pieces of jewelry looks quite different at the molecular level. With such a complicated collection of molecules, it's challenging to see the patterns, but look carefully - they are there!

One last pattern of crystal molecules:
This one is sugar! A selection of the pattern has been outlined in its center. You can then look at the entire picture and see the same pattern growing in every direction. Additionally, while this picture is 2D, sugar crystal molecules grow - of course - in 3 dimensions.

So what does any of this have to do with growing rock candy?

We know that pouring sugar into water will cause the sugar to dissolve, but when we pour sugar into hot water, the higher temperature causes more breaking apart of the sugar's molecular pattern. In other words, even more sugar dissolves in the water. But as the water cools, the separated sugar molecules re-form bonds with each other, forming a single and more massive pattern of molecules - rock candy!

The key to growing successful rock candy is creating a super-saturated solution of sugar water.
What does super-saturated mean?

In terms of sugar and water, a solution is saturated when you keep pouring and dissolving sugar into water up until the water cannot dissolve any more sugar. This point of equilibrium is saturation.

However, the hotter water can break apart more molecular patterns of sugar, allowing more sugar to be dissolved at the higher temperature than if the water was room temperature. This is super saturation. Then, once the water cools, it can no longer retain the same level of dissolved sugar. This forces the molecular patterns of sugar to reform, being "pushed out" from its dissolved state in water, and re-form as new crystals. 


Project Details


1. Begin by pre-heating the water. Measure 1 cup of water into a pot on a stove or hotplate and turn the heat up to its highest setting. Allow a few minutes for the water to heat up to an almost-boil, but not a full boil. Note: the water must be hot initially in order for achieve impressive results!

2. While the water is heating, prepare your popsicle sticks: Dip half of your popsicle sticks in water (of any temperature), then immediately dip into sugar. This will create a rough sugar surface that will make it easier for crystal sugar molecules to latch onto. Set your sugar-coated popsicle sticks aside on a plate and let dry.

3. Back to the pot. Once the water is hot, measure 3 cups of sugar. (This is also a good time to practice reading measurements on cups!) Pour the sugar into the hot water slowly and in intervals, stirring the sugar into the water consistently. Keep pouring slowly and keep stirring until all 3 cups of sugar are poured into the pot.

4. Once the water solution is super saturated, turn off the stove/hotplate and allow a few moments for the water to cool.

5. While the water is cooling, prepare the jars with food coloring: drop about 4 drops of food coloring into each jar. You can achieve rich basic colors by using all four of the same color drops, or get creative and mix them up!
Recommendation: using a lighter color such as yellow or red will allow you to better watch your crystals grow. If you want a dark purple rock candy, try making one jar purple but the other one yellow so that you can watch one of your candies grow!

6. Have the parent/adult pour the warm water solution equally into each jar.

7. Take each popsicle stick and clamp a clothespin at the very end of the non-sugar coated end. Stick each popsicle stick upside down inside a jar with the clothespin resting on top of the jar's opening. Ensure that the popsicle stick is about 1-2cm above the floor of the jar.
Note: If the popsicle stick is touching the bottom of the jar, change the grip of the clothespin on the popsicle stick such that the stick is higher up in the jar. If the popsicle stick is too close to the bottom of the jar, it may become stuck to the bottom of the jar and break your crystals when you try to remove it at the end.

8. Set the jars aside somewhere safe where they won't be touched or shaken for several days. The crystals must remain completely untouched or they won't grow as well!

9. Allow at least 3 days to grow and approximately up to 7 days total. If your experiment worked, you will start to see results even after just one day. Allowing more time for the crystals to grow means a bigger piece of candy at the end!

10. When you decide to retrieve your candy, use a butter knife to break the crystal coating on the top of the solution and gently pull out your popsicle stick. If your candy is stuck to the bottom of the jar, use the butter knife to chisel the bottom of the candy. You can also pour out the solution at this point for better chiseling visibility.

11. Enjoy!



Our brains better retain information when we engage both our hands and minds in the activity. Now that we've explained how to engage the hand, what are some discussion questions to engage the mind during the activity?

1. What if we want to make just 1 stick of rock sugar? How would we divide up the recipe?

2. What if we want to make an even number of rock sugar sticks (4, 6, 8...)? What values of sugar and water would we need?

3. What if we wanted to make an odd number of rock sugar sticks (3, 5, 7...)? How would we fix the recipe? What values of sugar and water would we need?

4. Now that we've created our own rock candy, how do you think crystal geodes are formed? What is in common between our home experiment and the awe-inspiring gems made by nature?

Supporting Resources

Here's a fantastically thorough article on the science behind growing your very own sugar rock crystals!:

Supporting Resources

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